There are known burners for cookers provided with two or three gas crowns, in particular burners with three crowns, a central one and two outer ones, one facing the inside and one facing the outside of the burner.
This type of burner enables uniform heating of the pans that are set on them irrespective of the shape and size of the pans.
In the European patent application EP 0 797 048 in the name of the present applicant, a burner with three gas crowns is described which is provided with a horizontal Venturi made in a chamber formed between a base of the burner and an upper portion comprising the central gas crown. The chamber of the Venturi communicates with an upper chamber defined by the bottom of the area of central crown and by the central burner cap. This burner is substantially formed by three die-cast pieces which are then assembled together.
In the European patent application 0 903 538 in the name of the present applicant, an improved burner is described, which likewise has the characteristic of comprising three concentric gas crowns and means for feeding the gas/primary air mixture to said crowns. The said burner is made up of just two die-cast pieces, and the chamber with Venturi effect, which is substantially horizontal, is defined by the surfaces set facing one another, one of which corresponding to the body of the burner and the other to the cap of the central gas crown. Notwithstanding the advantage of being made up of just two die-cast pieces, this burner presents, however, certain drawbacks; in particular, using just two die-cast pieces it is not possible to make, inside the burner, all the ducts necessary for the passage of the primary air and of the gas/primary air mixture. In fact, in this burner, the ducts that carry the gas/primary air mixture from the mixing chamber to the circumferential crowns are not altogether made in the body of the burner, but are defined by ducts delimited at the top only by planar appendages that join the central cap to the annular burner cap, a solution which is not ideal given the consequent inevitable leakages of mixture and the possibility of undesired displacements of said burner caps.